Field of the Invention
The present invention relates to a multilayer composite comprising a barrier layer of a partly aromatic polyamide and a layer of a moulding compound based on an impact-modified partly aromatic polyamide. The multilayer composite is primarily a hollow article, for instance a hollow profile or a container for conducting or storing liquid or gaseous media.
Discussion of the Background
The development of multilayer composites employed, for example, as pipes for conducting liquid or gaseous media in motor vehicles is subject to automotive industry demands for an improved barrier effect, for fuel lines in particular, to reduce emissions of fuel components into the environment as well as to requirements of sufficient fuel resistance. This has resulted in the development of multilayer pipe systems where, for example, fluoropolymers, ethylene vinyl alcohol copolymers (EVOH) or thermoplastic polyesters are employed as the barrier layer material. Additionally, WO 2005/018891 discloses hollow articles comprising at least one layer of an impact-modified partly aromatic polyamide and optionally one or more layers of aliphatic polyamide,
Multilayer composites composed of two different layers which are both based on a polyamide composed of an aromatic dicarboxylic acid and an aliphatic diamine having 9 to 13 carbon atoms, wherein the layer materials comprise different amounts of impact modifiers, are known from EP 1 864 796 A1 and JP 2009-119682 A. However in this solution the monomer basis on the diamine side is relatively costly. Such polyamides can moreover be processed only with difficulty which is manifested, for example, in insufficient dimensional accuracy during layer construction. A further disadvantage of these multilayer composites is their low elongation at break. For automotive applications a high elongation at break is required, so that in the event of an accident the fuel lines or similar lines remain undamaged. Thus, a pipe having a 800 μm—thick layer of an impact-modified PA9T and a 200 μm—thick layer of an ETFE is produced in comparative example 24 of US 2014/0299220 A1; the elongation at break here is 22%, However, in such pipes an elongation at break of more than 100% is desirable.